Manufacturing process for a plated product comprising a support part in steel and an anticorrosion metallic coating

ABSTRACT

The aim of the present invention is a process for manufacturing a plated product ( 1 ) comprising a support part in steel ( 2 ) and an anticorrosion metallic coating ( 3 ), characterized in that the anticorrosion coating ( 3 ) is fixed on the support part ( 2 ) by controlled-atmosphere brazing, in particular by vacuum brazing. The process according to the invention makes it possible to fix solidly an anticorrosion coating with a thickness smaller than 1 mm on a steel plate.

FIELD OF THE INVENTION

[0001] The present invention relates to devices for the handling,stocking and processing of chemical products intended for the chemicalindustries. In particular it concerns mixers, processing devices androuting devices capable of handling highly corrosive products, such asconcentrated acids or bases. In the present application, the expression“elements of chemical devices” means in particular, and in a collectivemanner, storage chambers, tanks, heat exchangers, mixers, treatmentdevices and routing devices.

[0002] More specifically, the invention relates to a manufacturingprocess for plated products comprising at least one support part insteel and an anticorrosion metallic coating, such as elements ofchemical devices or assembly parts intended for manufacturing elementsof chemical devices.

STATE OF THE ART

[0003] The chemical industries use numerous elements of chemicaldevices, which are needed for handling, stocking and/or processinghighly corrosive chemical products and which, consequently, have to becapable of resisting any attack from the latter.

[0004] In order to guarantee high resistance to corrosion, the elementsof the chemical device usually comprise steel support parts and ametallic anticorrosion coating with a base of so-called “noble” metals,such as titanium, tantalum, zirconium, a nickel-based alloy or stainlesssteel. The elements of the chemical device can be manufactured bymounting assembly parts, such as plates, previously coated with ananticorrosion metallic coating. The anticorrosion coating can be fixedto the support part in different ways, such as knurling, explosioncladding, hot rolling or simple covering without any junction betweenthe plate and the anticorrosion coating.

[0005] Certain applications, such as devices with low internal pressure,need a strong link between the steel support part and the anticorrosioncoating, that is to say a link with high resistance to stripping, inorder to avoid separation which could, for example, lead to collapse ofthe anticorrosion coating. Knurling, explosion cladding and hot rollingmake it possible to obtain very strong part/coating links, but thesetechniques can only be used when the thickness of the anticorrosioncoating is less than 0.7 mm.

[0006] The applicant therefore looked for a method applicable toindustrial development for fixing solidly a low thickness anticorrosioncoating on a support part in steel.

AIM OF THE INVENTION

[0007] The aim of the invention is a process for manufacturing a platedproduct comprising a support part in steel and an anticorrosion metalliccoating, such as an element of a chemical device or an assembly partintended to manufacture chemical device elements, characterized in thatthe anticorrosion coating is fixed on the support part by brazing undercontrolled atmosphere, such as vacuum brazing or brazing under inertgas.

[0008] The applicant noted that the process according to the inventionmade it possible to fix solidly on a metallic part in steel ananticorrosion coating with a thickness less than 1 mm, or even less than0.5 mm, possibly smaller than or equal to 0.3 mm.

FIGURES

[0009]FIG. 1 shows diagrammatically a product plated according to theinvention.

[0010]FIG. 2 shows diagrammatically an embodiment of the processaccording to the invention.

DESCRIPTION OF THE INVENTION

[0011] According to the invention, the process for manufacturing aplated product 1 comprising a support part in steel 2 and ananticorrosion metallic coating 3 is characterized in that it comprisesat least one controlled-atmosphere brazing operation, using at least onebrazing material 4, in such a way as to establish a mechanical linkbetween at least one defined part of the support 2 and at least onedefined part of the coating 3.

[0012] Said defined parts are called bonding surfaces. The link betweenthe support and the coating can be established by several bondingsurfaces. The bonding surface or surfaces are advantageouslypre-treated, before the brazing operation, in such a way, in particular,so as to eliminate the surface oxides. For example, one can carry out atleast one treatment selected from the chemical, the electrochemical, thephysico-chemical and the mechanical treatments (such as chemicalpickling, electrochemical pickling, machining or sanding). Thesetreatments may be combined.

[0013] In order to enhance the strength of the bonding the process ofthe invention may also comprise depositing at least one layer capable ofimproving the tying of the brazing material. The deposition can beeffected by chemical means, electrolytic means or in vapor phase(chemical vapor deposition or physical vapor deposition). Said layer istypically metallic, for example titanium or copper. The deposition maybe carried out on the support part 2, the metallic coating 3 or both.The deposition is effected before the brazing operation.

[0014] The brazing operation normally comprises bringing said definedparts together in such a way as to obtain a spacing D which ispreferentially chosen so as to avoid the formation of gas bubbles orbonding defects between the bonding surfaces during the brazingoperation. The spacing D is typically less than 0.1 mm. The appropriatevalue of the spacing D can be obtained by applying a plating pressure onthe support and the coating.

[0015] The controlled atmosphere may be a vacuum (at least partial) oran inert gas (such as a rare gas (typically argon or helium) or nitrogenor a mixture thereof).

[0016] The brazing under controlled atmosphere is preferably vacuumbrazing. Preferably the vacuum is fairly high, that is to say that theresidual pressure in the chamber is less than 10⁻⁴ mbar, and typicallyis comprised between 10⁻⁴ and 10⁻⁵ mbar. This embodiment makes itpossible to avoid contamination of the elements of the assembly and/orpossible pollution by the gas of the controlled atmosphere (which may,for example, weaken the metallic coating at the brazing temperature(typically by the action of oxygen possibly contained in the industrialinert gases)).

[0017] In the preferred embodiment of the invention, saidcontrolled-atmosphere brazing operation comprises:

[0018] interposing at least one brazing material 4 between the steelsupport part 2 and the anticorrosion coating 3, in such a way as to forman initial assembly 5;

[0019] possibly, applying a plating pressure on said initial assembly 5;

[0020] introducing the initial assembly into a controlled-atmospherechamber, such as a vacuum chamber, 10 provided with means of heating 11such as a resistance;

[0021] controlling the atmosphere in the chamber 10 (and thus inproximity to said assembly), such as forming a vacuum in said chamber orreplacing the atmosphere in said chamber with an inert gas;

[0022] heating of said assembly 5 up to a temperature at least equal tothe brazing temperature of said brazing material 4.

[0023] The brazing temperature, typically equal to the fusiontemperature of the brazing material, is such that the material melts andproduces an intimate bond with the element in contact with it (steelsupport part and/or anticorrosion coating).

[0024] The brazing material is preferably spread uniformly between thesupport part and the anticorrosion coating in order to obtain a uniformbonding layer and to increase the contact surface between these twoelements.

[0025] Interposing the brazing material 4 between the support part 2 andthe anticorrosion coating 3 can be carried out in two stages. Inparticular, the interposing can comprise:

[0026] depositing the brazing material 4 on the support part 2, at thelocation of the so-called “bonding” surface;

[0027] positioning of the anticorrosion coating 3 on the support part 2,in such a way as to form said initial assembly 5.

[0028] In certain cases, it can be advantageous to first carry out thedeposit of the brazing material 4 on the anticorrosion coating 3, levelwith the so-called “bonding” surface, and then to position the supportpart 2 on the anticorrosion coating, in such a way as to form saidinitial assembly 5.

[0029] Advantageously one can apply a mechanical plating pressure onsaid assembly before and/or during said re-heating. This platingpressure is exercised so that the support part and the anticorrosioncoating are tightened against each other so as to compress the brazingmaterial.

[0030] Preferably, the anticorrosion metallic coating 3 is in titanium,an alloy of titanium, tantalum, an alloy of tantalum, zirconium or analloy of zirconium.

[0031] The brazing material 4 can be a fusible alloy (typically aneutectic alloy) or a fusible metal. Said material 4 can possibly containa flux. Advantageously the brazing material can diffuse in the elementwith which it is in contact, which makes it possible to ensure a verystrong bonding between said elements. The brazing material is typicallyin the form of a powder, a sheet or a mesh. In its trials, the applicantnoted that the mesh presented the advantage of compensating efficientlyfor any possible variation in spacing D between the bonding surfaces.

[0032] When the coating 3 is in tantalum or an alloy of tantalum, thebrazing material 4 is typically composed of nickel, chromium, silicon orboron, or a mixture or an alloy thereof, such as an alloy of the BNitype containing nickel and boron (according to ASTM classification),such as Ni-14Cr-3B-4.5Si-4Fe, Ni-7Cr-3B-4.5Si-3Fe or Ni-2B-3.5Si-1.5Fe.In these cases, the brazing temperature is situated typically between1000° and 1050° C. The brazing material 4 may also be a silver-basedmaterial (such as an alloy or a mixture) containing lithium, copper,aluminium, zinc and/or tin.

[0033] When the coating 3 is titanium or an alloy of titanium, thebrazing material 4 is typically a silver-based material (such as analloy or a mixture) containing lithium, copper, aluminium, zinc and/ortin, or an alloy with a titanium base, such as TiNi, TiZrBe,48Ti-48Zr-4Be or 43Ti-43Zr-12Ni-2Be.

[0034] When the coating 3 is zirconium or an alloy of zirconium, thebrazing material 4 is typically an alloy with a base of zirconium,copper or nickel, such as Zr-5Be, Cu-20Pd-3In, Ni-20Pd-10Si,Ni-30Ge-13Cr or Ni-6P. The brazing material 4 may also be a silver-basedmaterial (such as an alloy or a mixture) containing lithium, copper,aluminium, zinc and/or tin.

[0035] The steel support parts and the anticorrosion coatings can takethe form of plates. These elements, which can be cut out beforehand, aretypically flat, but they can also be rounded, half-cylindrical oranother shape. The elements can also be shaped before being bonded bybrazing. It is also possible to carry out a brazing on a chemical deviceelement using anticorrosion metallic coatings with an appropriate shape.

[0036] The steel used is generally a carbon steel, and preferably achromium steel. It is particularly advantageous to use a steel whosethermal expansion coefficient is close to that of the anticorrosioncoating, that is to say that, advantageously, the difference between thethermal expansion coefficient of said steel and the expansioncoefficient of the anticorrosion coating is less than 20% and preferablylower than 10%. More precisely, the thermal expansion coefficient ofsaid steel is equal to that of said coating ±20% and preferably ±10%.

[0037] The support part 2 and/or the anticorrosion coating can bepresented in the form of a plate or sheet.

[0038] Said plated product 1 can be an assembly part or a chemicaldevice element.

EXAMPLES Trials 1

[0039] Trials on manufacturing assembly parts were carried out by vacuumbrazing using plates in carbon steel and anticorrosion coatings intantalum. The brazing material was a BNi alloy of the ASTMclassification, with a nickel base and containing boron, chromium andsilicon.

[0040] The values of resistance to stripping observed during thesetrials were between those obtained on assembly parts produced byexplosion cladding and those obtained on assembly parts produced byknurling.

[0041] The applicant noted that the depth of diffusion of the brazingmaterial in the tantalum element was of the order of 10 to 20 μm, suchthat the resistance to corrosion of the tantalum coating was notaffected by this diffusion.

[0042] Trials 2

[0043] Trials on manufacturing assembly parts were also carried out byvacuum brazing using plates in carbon steel and anticorrosion coatingsin either tantalum or titanium. The brazing material had a silver andcopper base.

[0044] Bending and punching tests (with a curvature radius varyingbetween 30 mm and 100 mm) have shown no breaking or decoherence of thebrazing bond which exhibited a low relative hardness (110 Hv). Moreovercalendering of titanium plates (with dimensions 1 m×1 m) was done with aradius of curvature equal to 150 mm without degrading the quality of thebond (even at a microscopic scale).

[0045] The applicant further noticed that the diffusion depth of thebrazing material 4 in the anti-corrosion coating 3 was lower than 60 μm,so that the resistance to corrosion is not affected by this diffusion.

Advantages of the Invention

[0046] The plated products obtained by the process of the inventionpresent the advantage of high transversal thermal conductivity thanks toa close bonding between the support part and the anticorrosion coatingover the greater part of the bonding surface, which is not the case, forexample, with a bond obtained by knurling which only produces bondingbands. Transversal thermal conductivity is particularly advantageous inchemical devices comprising means of thermal transfer such as anexchanger or a double envelope for cooling or heating.

1. A process for manufacturing a plated product comprising a supportpart in steel and an anticorrosion metallic coating, said processcomprising at least one brazing operation under controlled atmosphere,utilizing at least one brazing material, in such a way as to establish amechanical bond between at least one defined part of the support and atleast one defined part of the coating.
 2. The manufacturing process ofclaim 1, wherein the brazing operation comprises bringing said definedparts closer together in such a way as to obtain a space D less than 0.1mm.
 3. The manufacturing process of claim 1, wherein the brazingoperation is effected under vacuum.
 4. The manufacturing process ofclaim 3, wherein the residual pressure of said vacuum is less than 10⁻⁴mbar.
 5. The manufacturing process of claim 3, wherein said brazingoperation comprises: interposing at least one brazing material betweenthe steel support part and the anticorrosion coating, in such a way asto form an initial assembly; optionally, applying a plating pressure onsaid initial assembly; introducing the initial assembly into a vacuumchamber provided with means of heating; formation of a vacuum in saidchamber; heating of said assembly up to a temperature at least equal tothe brazing temperature of said brazing material.
 6. The manufacturingprocess of claim 1, wherein the brazing operation is effected underinert gas.
 7. The manufacturing process of claim 6, wherein the inertgas is selected from the group comprising rare gases, nitrogen andmixtures thereof.
 8. The manufacturing process of claim 6, wherein saidbrazing operation comprises: interposing at least one brazing materialbetween the steel support part and the anticorrosion coating, in such away as to form an initial assembly; possibly, applying a platingpressure on said initial assembly; introducing the initial assembly intoa controlled-atmosphere chamber provided with means of heating;replacing the atmosphere in said chamber with an inert gas; heating ofsaid assembly up to a temperature at least equal to the brazingtemperature of said brazing material.
 9. The manufacturing process ofclaim 1, further comprising at least one treatment selected from thegroup comprising the chemical treatments, the electrochemicaltreatments, the physico-chemical treatments, the mechanical treatmentsand the combinations thereof.
 10. The manufacturing process of claim 1,further comprising depositing at least one layer capable of improvingthe tying of the brazing material.
 11. The manufacturing process ofclaim 10, wherein said layer is metallic.
 12. The manufacturing processof claim 10, wherein said depositing is effected by chemical means,electrolytic means or in vapor phase.
 13. The manufacturing process ofclaim 1, wherein the thickness of said coating is less than 1 mm. 14.The manufacturing process of claim 1, wherein the thickness of saidcoating is less than 0.5 mm.
 15. The manufacturing process of claim 1,wherein said coating is in tantalum or an alloy of tantalum.
 16. Themanufacturing process of claim 15, wherein the brazing material is amaterial containing nickel and boron.
 17. The manufacturing process ofclaim 15, wherein the brazing material is a silver-based materialcontaining lithium, copper, aluminium, zinc and/or tin.
 18. Themanufacturing process of claim 1, wherein said coating is in titanium oran alloy of titanium.
 19. The manufacturing process of claim 18, whereinthe brazing material is an alloy with a titanium base.
 20. Themanufacturing process of claim 18, wherein the brazing material is asilver-based material containing lithium, copper, aluminium, zinc and/ortin.
 21. The manufacturing process of claim 1, wherein said coating isin zirconium or an alloy of zirconium.
 22. The manufacturing process ofclaim 21, wherein the brazing material is an alloy with a base ofzirconium, copper or nickel.
 23. The manufacturing process of claim 21,wherein the brazing material is a silver-based material containinglithium, copper, aluminium, zinc and/or tin.
 24. The manufacturingprocess of claim 1, wherein the brazing material comes in the form ofpowder, a sheet or a mesh.
 25. The manufacturing process of claim 1,wherein said steel is a chromium steel.
 26. The manufacturing process ofclaim 1, wherein the difference between the thermal expansioncoefficient of said steel and the thermal expansion coefficient of saidanticorrosion coating is less than 20%.
 27. The manufacturing process ofclaim 1, wherein said support part comes in the form of a plate orsheet.
 28. The manufacturing process of claim 1, wherein said coatingcomes in the form of a plate or sheet.
 29. The manufacturing process ofany one of claims 1 to 28, wherein said plated product is an assemblypart or an element of a chemical device.